There are cover versions and there are mash-ups.
But there are cover versions that make you hear a song in a whole new light - and there are mash-ups to make your spine tingle.
And there are also famous songs transposed into major or minor scales - or even simply slowed down - to glorious, spooky effect.
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From Dolly to Britney, The Beatles to Daft Punk, we've rounded up some of our favourite YouTube song transformations, below. Enjoy! And try to sing along. If you can...